set.rkt

#lang racket
(define (element-of-set? x set)
    (cond ((null? set) false)
          ((equal? x (car set)) true)
          (else (element-of-set? x (cdr set)))))

(define (adjoin-set x set)
    (if (element-of-set? x set)
        set
        (cons x set)))

(define (intersection-set set1 set2)
    (cond ((or (null? set1) (null? set2)) '())
          ((element-of-set? (car set1) set2)
              (cons (car set1) (intersection-set (cdr set1) set2)))
          (else (intersection-set (cdr set1) set2))))
(define (union-set set1 set2)
    (cond ((null? set1) set2)
          ((null? set2) set1)
          (element-of-set? (car set1) set2)
              (union-set (cdr set1) set2)
          (else (cons (car set1) (union-set (cdr set1) set2)))))
(define (iterate f x l)
    (cond ((null? l) ((f x (car l)) true)
    (else (iterate x (cdr l))))))